1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly relates to a semiconductor device having a high-dielectric-constant gate insulating film and to a manufacturing method thereof.
2. Description of the Related Art
Development of Si-LSI has been achieved by a size reduction of elements in accordance with a scaling law. According to this scaling law, a gate insulating film in a next-generation MOS-type field effect transistor having a gate length less than 0.1 μm is required to have a film thickness of 1.5 nm or less in terms of an equivalent thickness of SiO2.
In a case of SiO2, leakage current due to direct tunnel current cannot be restrained in an area of this film thickness, and this increases power consumption, so that SiO2 cannot be applied as the gate insulating film any longer in a next generation. Thus, to provide an alternative material, research and development have been intensively conducted for a high-dielectric-constant insulating film, that is, a high-k film which has a high dielectric constant and an increased film thickness so that the leakage current can be restrained, and many high-k materials have been proposed so far (e.g., refer to IEDM Tech. Dig. (2003) 107.).
However, in most of the high-k films heretofore proposed, the high-k film reacts with a Si substrate to generate a low-dielectric-constant interfacial layer at an interface therebetween. The generation of the undesired low-dielectric-constant interfacial layer is caused by a heat treatment during or after film formation. The generation of the low-dielectric-constant interfacial layer then results in a decrease in the dielectric constant as the gate insulating film, which is a primary factor preventing utilization of the high-dielectric-constant characteristics intrinsic to the high-k material.
There has thus been a demand to achieve a semiconductor device and a manufacturing method thereof which prevent the generation of the low-dielectric-constant interfacial layer during the film formation, can also restrain the generation of the low-dielectric-constant interfacial layer after the heat treatment and effectively use the high-k film as the gate insulating film.